[Git][ghc/ghc][master] 10 commits: Refactor fundep solving

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: fcf6331e by Richard Eisenberg at 2025-11-03T08:33:05+00:00 Refactor fundep solving This commit is a large-scale refactor of the increasingly-messy code that handles functional dependencies. It has virtually no effect on what compiles but improves error messages a bit. And it does the groundwork for #23162. The big picture is described in Note [Overview of functional dependencies in type inference] in GHC.Tc.Solver.FunDeps * New module GHC.Tc.Solver.FunDeps contains all the fundep-handling code for the constraint solver. * Fundep-equalities are solved in a nested scope; they may generate unifications but otherwise have no other effect. See GHC.Tc.Solver.FunDeps.solveFunDeps The nested needs to start from the Givens in the inert set, but not the Wanteds; hence a new function `resetInertCans`, used in `nestFunDepsTcS`. * That in turn means that fundep equalities never show up in error messages, so the complicated FunDepOrigin tracking can all disappear. * We need to be careful about tracking unifications, so we kick out constraints from the inert set after doing unifications. Unification tracking has been majorly reformed: see Note [WhatUnifications] in GHC.Tc.Utils.Unify. A good consequence is that the hard-to-grok `resetUnificationFlag` has been replaced with a simpler use of `reportCoarseGrainUnifications` Smaller things: * Rename `FunDepEqn` to `FunDepEqns` since it contains multiple type equalities. Some compile time improvement Metrics: compile_time/bytes allocated Baseline Test value New value Change ---------------------- -------------------------------------- T5030(normal) 173,839,232 148,115,248 -14.8% GOOD hard_hole_fits(normal) 286,768,048 284,015,416 -1.0% geo. mean -0.2% minimum -14.8% maximum +0.3% Metric Decrease: T5030 - - - - - 231adc30 by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 QuickLook's tcInstFun should make instantiation variables directly tcInstFun must make "instantiation variables", not regular unification variables, when instantiating function types. That was previously implemented by a hack: set the /ambient/ level to QLInstTyVar. But the hack finally bit me, when I was refactoring WhatUnifications. And it was always wrong: see the now-expunged (TCAPP2) note. This commit does it right, by making tcInstFun call its own instantiation functions. That entails a small bit of duplication, but the result is much, much cleaner. - - - - - 39d4a24b by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Build implication for constraints from (static e) This commit addresses #26466, by buiding an implication for the constraints arising from a (static e) form. The implication has a special ic_info field of StaticFormSkol, which tells the constraint solver to use an empty set of Givens. See (SF3) in Note [Grand plan for static forms] in GHC.Iface.Tidy.StaticPtrTable This commit also reinstates an `assert` in GHC.Tc.Solver.Equality. The test `StaticPtrTypeFamily` was failing with an assertion failure, but it now works. - - - - - 2e2aec1e by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Comments about defaulting representation equalities - - - - - 52a4d1da by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Improve tracking of rewriter-sets This refactor substantially improves the treatment of so-called "rewriter-sets" in the constraint solver. The story is described in the rewritten Note [Wanteds rewrite Wanteds: rewriter-sets] in GHC.Tc.Types.Constraint Some highlights * Trace the free coercion holes of a filled CoercionHole, in CoercionPlusHoles. See Note [Coercion holes] (COH5) This avoids taking having to take the free coercion variables of a coercion when zonking a rewrriter-set * Many knock on changes * Make fillCoercionHole take CoercionPlusHoles as its argument rather than to separate arguments. * Similarly setEqIfWanted, setWantedE, wrapUnifierAndEmit. * Be more careful about passing the correct CoHoleSet to `rewriteEqEvidence` and friends * Make kickOurAfterFillingCoercionHole more clever. See new Note [Kick out after filling a coercion hole] Smaller matters * Rename RewriterSet to CoHoleSet * Add special-case helper `rewriteEqEvidenceSwapOnly` - - - - - 3e78e1ba by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Tidy up constraint solving for foralls * In `can_eq_nc_forall` make sure to track Givens that are used in the nested solve step. * Tiny missing-swap bug-fix in `lookup_eq_in_qcis` * Fix some leftover mess from commit 14123ee646f2b9738a917b7cec30f9d3941c13de Author: Simon Peyton Jones Date: Wed Aug 20 00:35:48 2025 +0100 Solve forall-constraints via an implication, again Specifically, trySolveImplication is now dead. - - - - - 973f2c25 by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Do not treat CoercionHoles as free variables in coercions This fixes a long-standing wart in the free-variable finder; now CoercionHoles are no longer treated as a "free variable" of a coercion. I got big and unexpected performance regressions when making this change. Turned out that CallArity didn't discover that the free variable finder could be eta-expanded, which gave very poor code. So I re-used Note [The one-shot state monad trick] for Endo, resulting in GHC.Utils.EndoOS. Very simple, big win. - - - - - c2b8a0f9 by Simon Peyton Jones at 2025-11-03T08:33:05+00:00 Update debug-tracing in CallArity No effect on behaviour, and commented out anyway - - - - - 9aa5ee99 by Simon Peyton Jones at 2025-11-03T08:33:28+00:00 Comments only -- remove dangling Note references - - - - - 6683f183 by Simon Peyton Jones at 2025-11-03T08:33:28+00:00 Accept error message wibbles - - - - - 94 changed files: - compiler/GHC/Core/Opt/CallArity.hs - compiler/GHC/Core/Opt/Simplify/Iteration.hs - compiler/GHC/Core/Opt/Simplify/Utils.hs - compiler/GHC/Core/TyCo/FVs.hs - compiler/GHC/Core/TyCo/Rep.hs - compiler/GHC/Core/TyCon.hs - compiler/GHC/Iface/Tidy/StaticPtrTable.hs - compiler/GHC/Runtime/Eval.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/Expr.hs - compiler/GHC/Tc/Gen/Sig.hs - compiler/GHC/Tc/Instance/FunDeps.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - + compiler/GHC/Tc/Solver/FunDeps.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Irred.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Solver/Solve.hs - compiler/GHC/Tc/Solver/Solve.hs-boot - compiler/GHC/Tc/Types.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/Evidence.hs - compiler/GHC/Tc/Types/Origin.hs - compiler/GHC/Tc/Utils/Concrete.hs - compiler/GHC/Tc/Utils/Instantiate.hs - compiler/GHC/Tc/Utils/Monad.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/TcType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Zonk/TcType.hs - compiler/GHC/Tc/Zonk/Type.hs - compiler/GHC/Types/Basic.hs - compiler/GHC/Types/Unique/DSM.hs - + compiler/GHC/Utils/EndoOS.hs - compiler/ghc.cabal.in - testsuite/tests/count-deps/CountDepsAst.stdout - testsuite/tests/count-deps/CountDepsParser.stdout - testsuite/tests/default/default-fail05.stderr - testsuite/tests/dependent/should_fail/T13135_simple.stderr - testsuite/tests/deriving/should_fail/T3621.stderr - testsuite/tests/indexed-types/should_fail/T14369.stderr - testsuite/tests/indexed-types/should_fail/T1897b.stderr - testsuite/tests/linters/notes.stdout - testsuite/tests/parser/should_fail/RecordDotSyntaxFail10.stderr - testsuite/tests/parser/should_fail/RecordDotSyntaxFail13.stderr - testsuite/tests/parser/should_fail/T20654a.stderr - testsuite/tests/partial-sigs/should_fail/T14584a.stderr - testsuite/tests/polykinds/T6068.stdout - testsuite/tests/quantified-constraints/T15359.hs - testsuite/tests/rep-poly/RepPolyNPlusK.stderr - testsuite/tests/rep-poly/RepPolyRightSection.stderr - testsuite/tests/rep-poly/T13233.stderr - testsuite/tests/rep-poly/T19709b.stderr - testsuite/tests/rep-poly/T23903.stderr - testsuite/tests/typecheck/no_skolem_info/T13499.stderr - testsuite/tests/typecheck/should_compile/T13651.hs - − testsuite/tests/typecheck/should_compile/T13651.stderr - + testsuite/tests/typecheck/should_compile/T14745.hs - testsuite/tests/typecheck/should_compile/all.T - testsuite/tests/typecheck/should_compile/hole_constraints_nested.stderr - testsuite/tests/typecheck/should_compile/tc126.hs - testsuite/tests/typecheck/should_fail/AmbigFDs.hs - − testsuite/tests/typecheck/should_fail/AmbigFDs.stderr - testsuite/tests/typecheck/should_fail/FD3.stderr - testsuite/tests/typecheck/should_fail/FDsFromGivens2.stderr - testsuite/tests/typecheck/should_fail/T13506.stderr - testsuite/tests/typecheck/should_fail/T16512a.stderr - testsuite/tests/typecheck/should_fail/T18851b.hs - − testsuite/tests/typecheck/should_fail/T18851b.stderr - testsuite/tests/typecheck/should_fail/T18851c.hs - − testsuite/tests/typecheck/should_fail/T18851c.stderr - testsuite/tests/typecheck/should_fail/T19415.stderr - testsuite/tests/typecheck/should_fail/T19415b.stderr - testsuite/tests/typecheck/should_fail/T22684.stderr - + testsuite/tests/typecheck/should_fail/T23162a.hs - + testsuite/tests/typecheck/should_fail/T23162a.stderr - testsuite/tests/typecheck/should_fail/T25325.stderr - testsuite/tests/typecheck/should_fail/T5246.stderr - testsuite/tests/typecheck/should_fail/T5978.stderr - testsuite/tests/typecheck/should_fail/T7368a.stderr - testsuite/tests/typecheck/should_fail/T7696.stderr - testsuite/tests/typecheck/should_fail/T8603.stderr - testsuite/tests/typecheck/should_fail/T9612.stderr - testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.stderr - testsuite/tests/typecheck/should_fail/all.T - testsuite/tests/typecheck/should_fail/tcfail122.stderr - testsuite/tests/typecheck/should_fail/tcfail143.stderr The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/86c8274513318478b77d4286c2783ac... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/86c8274513318478b77d4286c2783ac... You're receiving this email because of your account on gitlab.haskell.org.